Historian Robert Beachy is the author of the new book "Gay Berlin: Birthplace of A Modern Identity," about the gay subculture that flourished in Berlin between World War I and the rise of the Nazis.
Secret life of the cat: The science of tracking our pets
They share our homes, sleep on our beds and occasionally bring unwanted gifts. Yet, despite our domestic cats playing a big role in our lives, we know surprisingly little about what they get up to. A research project by BBC2's Horizon and the Royal Veterinary College set out to find out more. Alan Wilson, a professor specialising in animal movement, describes what was involved.